On Jan. 15, 2025, the California Department of Public Health (CDPH) reported thatqOne confirmed human infection with influenza A(H5) virus was reported during the week.

The case occurred in a child less than 18 years old with no known contact with influenza A(H5N1) virus-infected animals or humans. The investigation into the source of infection for this case is ongoing, and no human-to-human transmission has been identified.

A specimen from the individual was tested at a public health laboratory using the Centers for Disease Control and Prevention (CDC) influenza A(H5) assay before being sent to CDC for further testing. The specimen was positive for influenza A(H5) virus using diagnostic RT-PCR. Additional analysis including genetic sequencing is underway. In response to this detection, additional case investigation and contact monitoring are being conducted by public health officials in California.